1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, or a facsimile device, and more particularly to a belt moving device such as an intermediate transfer belt or a sheet conveyor belt used in the image forming apparatus.
2. Description of the Related Art
In this type of belt moving device, a shifting guide is provided on an end surface of the belt to suppress belt shifting when the belt is driven. However, the straightness of the shifting guide is approximately 200 μm/1200 mm, and therefore the belt meanders, leading to deviation in the belt position as the driving time lengthens. In a tandem type color copier, for example, belt meandering of this type causes registration variation in the main scanning direction of a formed image. Hence, in a conventional belt moving device, the belt traveling speed is typically controlled, as described in publications such as Japanese Unexamined Patent Application Publication 2005-091943, Japanese Unexamined Patent Application Publication H06-263281, and Japanese Unexamined Patent Application Publication 2003-241535.
However, as will be described below, it is difficult to achieve control with a satisfactory degree of precision in the conventional belt moving devices described in these publications, and as a result, color shift occurs in both the main scanning direction and the sub-scanning direction of the formed image. Accordingly, high quality images cannot be obtained.